Original research articleSpatiotemporal patterns of vegetation phenology change and relationships with climate in the two transects of East China

Changes in vegetation phenology due to global climate change directly impact the dynamic balance of terrestrial carbon and nutrients and the biodiversity pattern, and send feedbacks to climate system. It is crucial to understand spatiotemporal patterns and mechanisms of vegetation phenology change and their relationship with climatic change. In this paper, we quantified the spatiotemporal patterns of start and end of growing season for seven vegetation types in Northeast China Transect (NECT) and North-South Transect of East China (NSTEC) during 2001-2013 using MODIS Enhanced Vegetation Index (EVI). The integral of EVI during growing season was also calculated as an additional phenological index. We then proceeded to analyze the relationship between the three phenological metrics and climate variables including daytime and nighttime temperature and precipitation. To study the temporal phenological trend of deciduous broadleaved forest in northeast China, we identified stands of deciduous broadleaved forest without land cover changes during 2001-2013 and derived the slopes of temporal changes in phenological metrics. Regression was applied to quantify the relationship between phenological trends and trends of climate variables.The vegetation types along the two transects in eastern China have distinctly different phenological characteristics and the strength of climate modulations on phenology varies among vegetation types. The study of temporal trend of phenological changes of the deciduous broadleaved forest in northeast China revealed that nighttime temperature is the most important driver. Increasing in nighttime temperature in spring tends to advance the start of growing season, while increasing in nighttime temperature during growing season tends to delay the growing season. Cold daytime prior to growing season also favors advanced start of growing season. On the other hand, summer nighttime temperature tends to bring down, whereas precipitation tends to enhance, the maximum EVI and hence the EVI integral as the latter is mostly determined by maximum EVI and to a less extent by length of growing season.